Misc bug-fix contributions

[Gollimnar]

I have a few bug fixes for web/screensaver.js [964affc]:

• Video error events in pre-player don't log the reason message.
• Clearing video src attribute triggers phantom error events.
• prepVideo() doesn't handle missing IDs cleanly.
• fade/down and wipe/down transitions should be fade/bottom and wipe/bottom, and throw exceptions as a result.
• drawVideo() transition exceptions freeze the screensaver.
• IPC 'blankTheScreen' events repeat, causing repeated fadeout effects.

If you're interested, I'll either need permission to open a branch and make a pull request, or possibly just attach the screensaver.js file for review.

[OrangeJedi]

This is awesome! Thanks for taking the time to hunt all of those bugs down. I would love the help to improve the project. Previously the best way to contribute has been to fork the repo and open a pull request from the fork (see this link).

I'm excited to see your work. I am working on a release for v1.3.0 right now and these fixes would be great to add in.